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Product information
21
April 2018
1
Plant density
Prof Below believes that producers don’t plant enough seed. He
says this has to change in order to obtain higher yields (
Photo 2
).
He believes this may be the South African producers’ problem,
whilst acknowledging the high cost of seed and the risks we face with
poor weather conditions.
Nonetheless he insists this factor has changed the most in the
USA over the last 55 years. The USA yield increases by 1 ton every
eight years. In 1965 the average yield was 4 t/ha (45 000 plants/ha
in 91 cm rows). Today the norm is 79 000 plants per ha in 76 cm
rows…‘and guess what, it’s only going to go up. It has to go up.’
Essentially grain yield is a product function of yield components:
Yield = plants/ha (planting and emergence) x kernels/plant (flower-
ing) x weight/kernel (grain filling). The function a producer has the
most control over is plants/ha. In the USA plant density increases
at a rate of 900 plants/ha/year despite high seed costs.
There is another factor to consider, i.e. maximum plant density.
Beyond 94 000 plants/ha in 76 cm rows plant competition decreases
yield. Prof Below says this will be reached within 15 years in the
USA then rows will have to become narrower, e.g. 51 cm. The future
of maize in South Africa has to be 76 cm rows. Narrower rows hold
two advantages: They can better manage the higher density of
plants and they intercept more early light.
A further benefit of narrow rows is higher moisture retention be-
cause the leaves shade the ground and prevent evaporation.
Tillage or no tillage
This is designed to control one of the preceding ‘wonders’ and can
influence yields by up to 0,9 t/ha.
Growth regulators
‘This is the next big thing in agriculture.’ This is all about leaf
health and leaf performance. Leaf greening is promoted through
the application of strobilurin fungicides which are applied even
in the absence of leaf disease. The greener leaves can give up to
0,6 t/ha increase in yield. There are risks which could decrease yields
if the wrong growth regulators are used in wrong conditions, i.e. be
very careful.
Table 1
sums up the seven wonders and their influence on yield
potential.
No maize plant left behind
Higher maize yields are achieved where a producer optimises each
of the seven wonders and their positive interactions and provides
better prerequisites, season long weed control (modern hybrids
don’t interact well with weeds) and balanced fertility.
Prof Below emphasised that in future both application and fertiliser
technologies will be used to supply the required crop nutrition.
Nutrients have a high harvest index value and producers must feed
the plant, not the soil.
He summarised with his four most important nutrients for high
grain yield namely, nitrogen, phosphorus, sulphur and zinc.
He advocates for fertilisation to be applied in bands – ‘where the
roots will be’ – as this results in an incredible improvement in the
early growth of the crop. A plant missing out on fertiliser is a plant
left behind and that plant will never catch up.
Understanding the factors that have the biggest impact on yield
gives growers the opportunity to increase yield.
1: Yield penalty due to residue.
2: Is the future of maize higher populations in narrow rows?
2
RANK
FACTOR
VALUE (T/HA)
1
Weather
4,4+
2
Nitrogen
4,4
3
Hybrid/variety
3,1
4
Previous crop
1,6
5
Plant density
1,3
6
Tillage/no-tillage
0,9
7
Growth regulators
0,6
Total
16,3
TABLE 1: THE SEVEN WONDERS OF MAIZE YIELD